The present invention relates generally to printing or marking apparatus and relates more particularly to apparatus for automatically marking individual items or units of production passing along a conveyor at a rapid rate. The present device has particular application in the manufacture of electrical components such as capacitors which are manufactured in large quantity by automatic equipment and which must be accurately printed with the manufacturer's name or symbol, a product number and/or an indication of its electrical characteristics.
High speed production techniques in many fields of manufacture have necessitated the development of printing machines which are utilized primarily at the finishing stages of production to provide either decorative or informational marking to a product. To avoid product rejection and to prevent production delays, it is essential that the printing or marking device be reliable, easily adjusted and readily cleaned and resupplied with the marking fluid, normally some type of permanent printing ink.
A wide variety of devices have been developed and utilized in the past for the application of decorative and identifying markings. In some cases, the ink is applied to the platen or type bearing the decorative or identifying marking and this in turn is brought into direct contact with the unit or article to be marked. Such devices suffer the disadvantage that the surface irregularities of the article to be marked result in unpredictable ink transfer, causing not only a poorly marked article but also leaving undesirable amounts of surplus ink on the marking element. Further, the direct contact of the marking element with the articles results in a rapid wear of the element and a consequent deterioriation of the mark quality.
A more advantageous but also more complicated and expensive arrangement provides for an offset printing whereby the image is transferred from the plate or type to a resilient roll or pad and is then transferred to the production articles. With such a system, the transfer of ink is more predictable and accurate and the transfer roll or pad can be resilient in nature so as to conform with surface irregularities of the item to be marked.
In addition to difficulties in transferring the inked image from the plate or type to the unit to be marked, a major source of problems with marking equipment has been the difficulty of applying a uniform coating of ink to the plate or type. The typical arrangement for this purpose has comprised an ink reservoir within which an ink drum is rotated with the ink layer thereon being regulated by a doctor blade. The ink from the ink drum is conventionally transferred to the plate or type by a rubber roller. Equipment of this type suffers from leakage of ink around the drum and blade and is difficult to clean at the end of a printing operation. Attempts have been made to design marking systems without the usual drum and reservoir including systems employing a rotating ink disc. However, these systems have also suffered from difficulties in accurately metering the ink to permit a transfer of a predetermined ink quantity to the plate or type.